FBI director James Comey confirmed Friday that his agency was treating the shooting spree in San Bernardino as a "federal terrorist investigation" but said there is no indication the killers were part of a cell or network or were directed by a terrorist group.

Authorities say Syed Farook, 28, and his wife, Tashfeen Malik, 27, opened fire on a holiday party at the Inland Regional Center in on Wednesday, killing 14 people and injuring 21. They were killed hours later in a gunbattle with police as they attempted to flee in a black SUV.

This undated combination of photos provided by the FBI, left, and the California Department of Motor Vehicles shows Tashfeen Malik, left, and Syed Farook.(Photo: AP)

Comey said there are indications of "radicalization by the killers and the potential inspiration by foreign terrorist organizations," but did not elaborate. U.S. officials earlier said Malik had expressed support for the Islamic State terrorist group and its leader, Abu Bakr al-Baghdadi, in a posting on Facebook.

While noting that the investigation is still in the early stages, Comey said "we have no indication that these killers are part of an organized, larger group or form part of a cell; there is no indication that they are part of a network."

Previously, authorities had declined to refer to the killings definitively as a terrorist act, suggesting they might have been triggered by a workplace dispute.

While conceding that a lot of evidence in this case that "does not make sense," Comey, speaking in Washington, said that a large volume of evidence prompted authorities to add the terror designation to the investigation.

"We are spending a tremendous amount of time trying to understand the motives of the killers and every detail of their lives," the FBI director said.

Comey said the killers tried to destroy or conceal evidence by smashing electronic devices, but that investigators had been able to harvest considerable data from cellphones. Authorities say Farook was deleting information from such devices at least one day before the attack.

Comey also sought to allay widespread concerns across the country over the killings.

"We know this is very unsettling for the people of the United States, but we hope you will not let fear becoming disabling, but try to channel it into an awareness of your surroundings," he said.

In a departure from comments earlier by the FBI in San Bernardino, Comey played down the possible importance of "telephonic connections" between the suspects and at least two subjects of earlier FBI investigations. Comey said that nothing about the contents of those communications elevated the California killers to the attention of the FBI prior to the attacks this week.

While there was no indication that the extremist group, also known as ISIL or ISIS, directed the massacre in California, Malik's Facebook posting, as described by U.S. officials, is the strongest link yet that the killings had terrorist roots.

The U.S. officials, who are not authorized to comment, said the posting that pledged support to al-Baghdadi was made under another name than Malik just before the shootings on Wednesday..

Al-Baghdadi, 44, became leader of the Al-Qaeda-affiliated group, Al-Qaeda in Iraq, in 2010. The group later spread into parts of Syria and in 2014 declared itself a caliphate, under the name Islamic State, with al-Baghdadi as the leader, or caliph.

Abu Bakr al-Baghdadi, shown in a file image taken from a video posted on a militant website in 2014, is the leader of the Islamic State extremist group.(Photo: AP)

As investigators delve into past travel, contacts and communications by the couple for clues to the shootings, family members say they are shocked and saw no sign that the American-born county health worker had been radicalized.

A search of a residential townhouse rented by the suspects turned up a staggering arsenal of firearms, thousands of rounds of ammunition, a dozen pipe bombs and a virtual bomb-making factory, police say.

Farook had attended a holiday party Wednesday at the Inland Regional Center then left briefly, returning with his wife to open fire on the group of friends and co-workers. They wore masks and tactical clothing and carried hundreds of rounds of ammunition. The pair also left a primitive pipe bomb,which did not detonate, before returning to their rental house and its stockpile of weapons.

"Clearly they were equipped and they could have done another attack," San Bernardino Police Chief Jarrod Burguan said Thursday. "We intercepted them before that happened, obviously."

This undated Student ID card photo from California State University, Fullerton, shows Syed Farook, one of the suspects in the Dec. 2, 2015, mass shooting in San Bernardino, Calif. The card was found in the Farook's apartment after the landlord allowed entry to members of the media.(Photo: AFP/Getty Images)

Investigators are examining evidence from three locations: the Inland Regional Center, where the killings occurred, the rented townhouse in nearby Redlands, and the rented black SUV in which the couple was fleeing when they were intercepted and killed in a gunbattle with police.

The FBI said it had completed its investigation at the couple's home, which was opened to the media Friday by the landlord.

The U.S.-born Farook worked as an environmental health specialist for San Bernardino County for five years, conducting health inspections. Farook's coworkers describe him as pleasant, but none of the colleagues contacted remember a lot about him.

Malik, 27, was born in Pakistan, entering the U.S. on a fiancée visa in 2014, the FBI says. The pair apparently met online, while she was living abroad.

Federal officials note that Farook had visited Saudi Arabia several times, including a trip in 2013 for the annual hajj, or pilgrimage, to Mecca that all Muslims are expected to complete at least once.

If he had become radicalized, his own family didn't appear to detect it.

Farook's brother in law, Farhan Kahn, expresses shock at the killings, calling the Farook he knew a "good religious person, just like a normal, anybody would be."

Asked by NBC News if Farook was someone who had been radicalized, he says, "Not the person I know. He was not radical."

He calls Farook simply a "bad person" for the attack, but says he has "no idea" what prompted it.

Federal Bureau of Investigation agents put up a screen to block the view of onlookers as they investigate the building at the Inland Regional Center were 14 people were killed in San Bernardino, Calif.
Joe Raedle, Getty Images

Shamshad Muscati, center, gets emotional during an interfaith memorial service at the Islamic Community Center of Redlands, in Loma Linda, Calif. The memorial service was held to honor the victims of the Dec. 3 shooting rampage that killed 14 people in San Bernardino, Calif.
Jae C. Hong, AP

San Bernardino Police Chief Jarrod Burguan takes a question at a press conference near the site of yesterday's mass shooting in San Bernardino, Calif. A heavily armed husband and wife dressed for battle opened fire on a holiday banquet for his co-workers Wednesday, killing multiple people and seriously wounding others in a precision assault, authorities said. Hours later, they died in a shootout with police.
Chris Carlson, AP

An officer stands guard at the police perimeter in a Redlands, Calif. neighborhood where a home linked to the suspects in the San Bernardino shooting rampage is located, in the early hours of Dec. 3, 2015.
Robyn Beck, AFP/Getty Images

Officers have their weapons drawn Wednesday as they surround the vehicle believed to be driven by the suspects involved in a military-style attack that killed multiple people and wounded others at a California center that serves people with developmental disabilities, authorities said.
KTTV via AP

Two women embrace at a community center where family members are gathering to pick up survivors after a shooting rampage that killed multiple people and wounded others at a social services center in San Bernardino.
Jae C. Hong, AP

A SWAT team arrives at the scene of a shooting in San Bernardino, Calif., on Dec. 2, 2015. Police responded to reports of an active shooter at a social services facility.
Doug Saunders, Los Angeles News Group, via AP

Nor does Farook's sister Saira Khan. "I can never imagine my brother or my sister-in-law doing something like this. Especially because they were happily married, they had a beautiful 6-month-old daughter," Khan, who is married to Farhan Khan, tells CBS News. "It's just mind boggling why they would do something like this."

When CBS reporter David Begnaud notes that people can't fathom how a couple could drop off their infant in the morning then go out and commit murder, Saira responds, "Yeah, we can't either,"

"It makes us very upset and angry that how could you leave a 6-month-old daughter," Farhan adds. "And he put us in this predicament," Saira says.

Authorities have been careful not to speculate as to whether the attack, which also left 21 people injured, was a terrorist act until the investigation is complete..

"We do not yet know the motive; we cannot rule anything out at this point," said Bowdich. "We don't know if this was the intended target or there was something that triggered him to do this immediately."

Lawyers for the family tell CNN that the family didn't know anything about Farook's deadly stockpile of ammunition.

The family was "completely shocked" to find out about Farook's involvement in the massacre, David S. Chesley, an attorney for Farook's family, tells CNN.

He says family member had ever seen Farook with any of the weapons found at the townhouse. "They haven't seen him with them, the pipe bomb, no one had ever seen him use or have anything like that."

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A look inside the apartment of Syed Rizwan Farook and Tashfeen Malik, the suspected shooters of killing 14 people and injuring many more during a shooting in San Bernardino, Calif.
Brett Kelman, The Desert Sun

A look inside the apartment of Syed Rizwan Farook and Tashfeen Malik, the suspected shooters of killing 14 people and injuring many more during a shooting in San Bernardino, Calif.
Brett Kelman, The Desert Sun

A look inside the apartment of Syed Rizwan Farook and Tashfeen Malik, the suspected shooters of killing 14 people and injuring many more during a shooting in San Bernardino, Calif.
Brett Kelman, The Desert Sun

A look inside the apartment of Syed Rizwan Farook and Tashfeen Malik, the suspected shooters of killing 14 people and injuring many more during a shooting in San Bernardino, Calif.
Brett Kelman, The Desert Sun

A look inside the apartment of Syed Rizwan Farook and Tashfeen Malik, the suspected shooters of killing 14 people and injuring many more during a shooting in San Bernardino, Calif.
Brett Kelman, The Desert Sun

Members of the media crowd into the apartment in Redlands, Calif. shared by San Bernardino shooting rampage suspects Syed Farook and his wife, Tashfeen Malik, Dec. 4, 2015, after the building landlord invited media into the townhouse rented by the California couple.
Getty Images

Members of the media crowd into the apartment in Redlands, Calif. shared by San Bernardino shooting rampage suspects Syed Farook and his wife, Tashfeen Malik, Dec. 4, 2015, after the building landlord invited media into the townhouse rented by the California couple.
Getty Images

Members of the media crowd into the living room of an apartment in Redlands, Calif., shared by San Bernardino shooting rampage suspects Syed Farook and his wife, Tashfeen Malik, Dec. 4, 2015, after the building landlord invited media into the townhouse rented by the California couple.
EPA

Members of the media crowd into the living room of an apartment in Redlands, Calif., shared by San Bernardino shooting rampage suspects Syed Farook and his wife, Tashfeen Malik, Dec. 4, 2015, after the building landlord invited media into the townhouse rented by the California couple. A book containing passages from the Quran is seen at right.
AP

Members of the media crowd into the living room of an apartment in Redlands, Calif., shared by San Bernardino shooting rampage suspects Syed Farook and his wife, Tashfeen Malik, Dec. 4, 2015, after the building landlord invited media into the townhouse rented by the California couple.
AP

Members of the media crowd into the living room of an apartment in Redlands, Calif., shared by San Bernardino shooting rampage suspects Syed Farook and his wife, Tashfeen Malik, Dec. 4, 2015, after the building landlord invited media into the townhouse rented by the California couple.
AP

Members of the media crowd into the living room of an apartment in Redlands, Calif., shared by San Bernardino shooting rampage suspects Syed Farook and his wife, Tashfeen Malik, Dec. 4, 2015, after the building landlord invited media into the townhouse rented by the California couple.
AP